John Mellencamp is apparently upset that Wisconsin Governor Scott Walker is using his song 'Small Town' at political rallies.

The Republican governor apparently played 'Small Town' at a Milwaukee campaign event ahead of his June 5 recall election.

A spokesperson for the singer has penned Governor Walker a personal letter to express Mellencamp's opposition to the politician's attempt to limit collective bargaining rights for government workers.

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Mellencamp apparently wrote to Governor Walker to make his dissent known, but did not ask the Republican to stop playing the song at his speeches.

"[John's] a very liberal person. He appeared at the Democratic National Convention in 2004. His wife at the time was a delegate at large," Mellencamp's rep told The AP. "He's very pro-collective bargaining and the fight for a living wageâ€¦ More often than not it's right wing candidates who use his songs, which is somewhat paradoxical."

'Small Town' featured on Mellencamp's 1985 album Scarecrow and reached the top five of the US singles chart. The song tells of Mellencamp's childhood in Indiana in a community populated by the working class.

Mellencamp's political advocacy dates back decades to his criticism of former US President Ronald Reagan in the 1980s.

The singer also co-founded Farm Aid in 1985 to raise money for struggling farmers and performed on the Vote For Change concert tour in opposition to George W Bush's re-election bid in 2004.